The invention relates to an arrangement with at least one workpiece to be sintered, in particular a dental workpiece, and with at least one supporting material and with a sintering apparatus for sintering the workpiece, wherein the sintering apparatus has at least one gas feed for protective gas and at least one base area, and the workpiece lies on the base area on the supporting material and protrudes at least partially beyond the supporting material. The invention also relates to a method for sintering at least one workpiece, in particular a dental workpiece, in a sintering apparatus.
For the sintering of workpieces, in particular dental workpieces, a wide variety of sintering apparatuses and also arrangements of the generic type have already been proposed in the prior art. In DE 20 2011 005 465 U1, concerning a different generic type, it is proposed for example to lower the workpieces to be sintered in an annular sintering tray completely within sintering granules, so that the sintering granules completely surround and cover the workpieces to be sintered during the sintering operation. It has been found from practical experience that, with this arrangement, the process of shrinkage of the workpiece that occurs during the sintering operation may be hindered, which leads to unwanted deformation of the workpiece. Arrangements of the generic type are disclosed for example in WO 2011/020688 A1. In this document it is proposed that a quartz tray should be filled during the operation of the sintering apparatus with inert beads, into which the article to be sintered is placed. To enter the quartz tray, that is to say the area around the workpiece to be sintered, the protective gas must flow around the quartz tray in order to enter the interior of the quartz tray from above. It has been found that, with this type of arrangement, a relatively great amount of protective gas is consumed during the sintering operation and impairments of the article to be sintered can nevertheless be caused by remnants of another gas, in particular oxygen.
In DE 10 2011 056 211, it is proposed to cover the tray in which the article to be sintered is located by means of a closure element, wherein the covered tray can be flowed through by protective gas or inert gas. However, it is not explained in detail in this document what form the covered tray should take to allow a flow to pass through it in this way.
DE 10 2009 019 041 A1, concerning a different generic type, concerns a sintering apparatus for sintering magnesium or magnesium alloys at relatively low sintering temperatures of 600° C. to 642° C. under a protective gas atmosphere. In FIG. 5 of this document, it is proposed to pass any impurities of the gas in the outer region of the crucible through getter material before this impurity can get into the inner region of the crucible.
Further sintering apparatuses are shown in DE 20 2010 007 606 U1 and JP S58 141305 A. In the Japanese document it is proposed to embed the workpieces to be sintered completely in the supporting material, or to lower them in it.
Extensive tests with a wide variety of sintering apparatuses have shown that even small changes in the structure of arrangements and sintering apparatuses of the generic type can often have an unexpectedly strong influence on the quality of the sintering result, in particular at very high sintering temperatures of sometimes over 1200° C. In particular, it is difficult with arrangements known in the prior art to ensure that no undesired discoloration or oxidation of the workpiece to be sintered occurs.